1. Field of the Invention
The present invention is related to orthopedic surgical instrumentation. In particular, the present invention is related to a unicondylar knee instrument system and a method of preparing a distal femur for the implantation of a unicondylar femoral implant.
2. Description of the Related Art
Orthopedic knee implant systems have been used for many years to treat patients with knee joints that have been damaged by trauma or disease, such as osteoarthritis, rheumatoid arthritis, and avascular neurosis. A knee arthroplasty resects, cuts, or resurfaces the damaged sections of the knee and replaces them with a prosthetic implant.
Most knee implant systems are tricompartmental implants and the surgical procedure used with tricompartmental implants is commonly known as total knee arthroplasty. These implants are known as tricompartmental implants because they are used when the femur is prepared to receive an implant by resurfacing or resecting the three compartments of the distal femur, i.e., the medial and lateral condyles and the trochlear groove. Regardless of the type of implant used, all arthroplasties require the bone to be specifically prepared to receive a corresponding implant by resecting, resurfacing, or deforming the bone to accept the implant.
Minimally invasive surgery (“MIS”) has become of great interest within the field of orthopedics. Thus, unicondylar or unicompartmental knee implants have become of great interest in the orthopedic industry due to their small size and applicability to MIS surgical approaches. Unicondylar knee implants are designed to replace only a single condyle (e.g., the medial or lateral condyle) of the distal femur.
Minimally invasive knee surgery has not yet been fully defined. However, minimally invasive knee surgery has generally been considered to include a smaller incision. A typical incision length for a total knee replacement can be up to 10 to 12 inches long. The general theory behind MIS is that with a smaller incision length, the patient will be able to recover from surgery faster.
Generally, the clinical outcomes for unicondylar knee implants have varied. Studies have reported long term survival rates for unicondylar implants to be less than that of comparable total knee implants. One particular cause for such discrepancies is due to the surgical technique associated with implanting the implant.
The unicompartmental implant most widely reported on is the Oxford implant. The Oxford implant is a mobile bearing unicompartmental implant that is implanted with a free-hand technique, i.e., where the bone resections are not guided by instrumentation. Thus, the clinical outcomes for these implants have in part been associated with a particular surgeon's ability in implanting the device. Accordingly, a surgeon proficient in this technique is more likely to have a better surgical outcome compared to a less experienced surgeon who is less technically proficient with the surgical technique for implanting the implant.
Recent advancements in unicondylar knee implants and instruments have resulted in instrumented techniques for implantation. U.S. Pat. No. 6,554,838 to McGovern et al. discloses a unicondylar knee implant that uses a guided burring technique to implant the femoral component. However, conventional instrumentation systems are bulky and are required to be operated from various angles as opposed to a single orientation. Such instrument designs are also not completely conducive to minimally invasive surgical approaches or a reproducible surgical result.
Thus, there is a need for a unicompartmental knee instrument system that addresses the above mentioned deficiencies in current instrument designs while simultaneously being suitable for minimally invasive surgical techniques.